1. Field of the Invention
The present invention relates to a method and an apparatus for inspecting a slider, and particularly relates to a method and an apparatus for optically inspecting a slider that is used for a hard disk drive.
2. Description of the Related Art
A slider is produced by forming a write element and a read element on a ceramics wafer, such as an AlTiC wafer, by means of the thin-film technology, then by dicing the wafer into bars such that the surface of the bar that is to be formed in an air bearing surface extends in the longitudinal direction of the bar, and further by dicing the bar into individual sliders. When a write element and a read element are formed on a wafer, the identification number of each slider is written on the top surface of the layers that are deposited, and the sliders are controlled by the identification numbers after the wafer is diced. After the sliders are separated from the wafer by dicing, each slider is subjected to visual inspections several times using an optical microscope or the like. The inspections are performed when the slider is included in a bar, when slider has been separated from the bar, and also when the slider has been incorporated in a head gimbal assembly (HGA). If the inspection is performed only at the final stage at which the slider has been incorporated into an HGA, then yield loss is increased, and investigation to determine the cause of defects cannot be performed effectively. Therefore, it is very important to perform inspection at each process in order to identify yield loss at each step, to identify the cause of defect, and to provide improvement in the process.
Visual inspection is performed mainly in order to find adhesion of dust to the air bearing surface or to the surface that is to be formed in the air bearing surface by means of lapping (hereinafter, called a first surface) and to find chippings on the first surface. However, it is necessary to simultaneously inspect the top surface of the layers together when the first surface is inspected because the slider number is written on the top surface of the layers. Further, in order to manage the manufacturing process of the bar, the slider number needs to be checked at each step. Indeed, the top surface of the layers is more frequently checked than the first surface. The slider number is checked by a microscope. In order to identify each slider, both the wafer number and the slider number are required. The wafer number is often written on the surface that is opposite to the top surface of the layers, i.e., on the back surface of the wafer. In this case, three surfaces in total including the first surface need be inspected by means of a microscope. In this specification, inspection of the slider means not only checking and inspecting the first surface and other surfaces, as well as performing visual inspections of the slider, but also merely checking the slider number and the wafer number.
Incidentally, since a bar is highly brittle, it is normally stored and conveyed in a case, or in a tray. FIG. 1 shows an exemplary tray which has been conventionally used. Tray 121 is made of a frame, in which a plurality of bars can be simultaneously stored. Stepped portions 123 are provided at two sides of the tray that are opposite to each other, and bars B are held by stepped portions 123. Since the slider numbers are frequently checked, as described above, bars B are held such that the top surface of the layers, on which the slider numbers are written, faces upward so that the slider numbers can be easily checked.
When the visual inspection of the first surfaces is performed, the slider numbers are first checked with an optical microscope in a state in which the bars are held in the tray. If the wafer number is written on the back surface of the wafer, then the tray is turned upside down in order to check the wafer number. Next, the bar is removed from the tray one by one by using tweezers, then conveyed to an inspection table on which an optical microscope is installed, and the first surfaces are inspected. However, the quality and efficiency of the inspection significantly depend on the skill (skill of positioning the bar, inspection time, etc.) of the operator, and there is large variability in the level of skill among the operators. Since the bar is bristle, the operation of removing a bar from a tray and of returning the bar to the tray after inspection requires immense skill, and damage to the bar that is caused by an operational error or by adhesion of contaminants to the bars frequently takes place, which leads to a reduction in yield and an increase in inspection time. If a defect is found on the first surface, then the bar is turned by 90 degrees to check the slider number again in order to identify the slider. If many defects are found, then the inspection time is increased. In order to shorten the inspection time, a larger number of operators are required.
In order to address the problem mentioned above, efforts have been made to rationalize the method for inspecting a slider. Japanese Patent Laid-Open Publication No. 223534/93 discloses a method for inspecting a slider in which a slider is inspected from a plurality of directions. Specifically, many slides are fixed to the outer peripheral surface of a rotating support element. The orientation of the sliders is changed in accordance with the rotation of the support element. A visual inspection is performed by means of a fixed camera. It is also disclosed that sliders are fixed to a tape in advance and then the tape is wound on the support element in order to fix the slider.
Japanese Patent Laid-Open Publication No. 2002-048716 discloses a method for simultaneously inspecting a plurality of surfaces of a slider by using mirrors. Specifically, mirrors each having angles of 45 degrees are arranged on the sides of a slider which is to be inspected. By arranging the mirrors within the field of view of an optical microscope, the images of the sides of the slider, which are the reflections in the mirrors, as well as the slider itself, come into the field of view of the optical microscope so as to allow the state of the sides, as well as the front surface, of the slider to be simultaneously inspected.
However, the conventional art which is disclosed in these patent documents is disadvantageous with regard to operation efficiency because the prior art requires separating a slider from a bar by dicing and then fixing the slider that is separated onto a special support tool. If adhesive is used to attach a slider to the support tool, then the adhesive may remain on the slider, and reliability of the slider may deteriorate.